ANALYSIS OF GENERATE MECHANISM OF RESIDUAL STRAIN IN CAST-IN-PLACE PILES

The residual strain in a pile markedly influences the axial force distributing curve of a pile, but it was rarely studied on cast-in-place piles. The strain state of a Multi-field coupling model for a pile before loading is first constructed. In the model, according to adding up the strain respectively produced by self-weight of a pile, concrete shrinkage, change of concrete temperature and creep, theory expressions for residual strain is derived, and its results fit close to monitoring results in construction practice. In succession, the differences between theory results and monitoring results are analyzed; the main influence factors for the differences are complicated boundary condition around piles and difficulties on measuring parameters of concrete in curing, and those factors limited application area of the theory expressions. Lastly, according to revising elastic modulus, the theory reaults fit closer to the monitoring results. In general, generate mechanism of residual strain in cast-in-place piles are elementarily explained，and it can also explain results of Kister G (2007). The residual strain of a cast-in-place pile has influence on the pile quality, bearing behavior on the pile body and bottom, and contact status between the pile side and rock around the pile, so it deserve to be noticed in construction practice.